Rupture-resistant fluid transport and containment system

ABSTRACT

Fluid transport and containment systems are protected from rupture related to an expanded volume within the systems. A fluid transport system, such as a water supply pipe, has a relief channel along its length configured for expanding outwardly when fluids contained in the pipe freeze and expand. A unitary pipe configuration including a pipe wall and an integral core structure that can be sealed at each end provides a means for expansion sufficient to resist freeze-induced rupture. Such pipe configurations can be used with conventional pipes and pipe fittings and with adapters adapted to fit both the improved pipes and conventional pipes and pipe fittings.

FIELD OF THE INVENTION

[0001] The present invention relates to protection of fluid transport and containment systems from rupture related to an increased internal volume. In particular, the present invention relates to a unitary pipe structure sufficiently expandable to resist rupture due to freezing of fluids within the system.

BACKGROUND OF THE INVENTION

[0002] It is well known that when water freezes to solid ice it undergoes an expansion in volume of about 9%. This physical change causes increased pressure within a water containment system or transport passage and has been the cause of many instances of bursting of water pipes. There have been many attempts to solve this problem. In residential housing the typical practice is to insulate water pipes or otherwise keep them from exposure to freezing temperatures by putting the pipes under ground or inside houses where a heating system maintains temperatures above freezing.

[0003] Another approach to protect pipes from freezing is covering pipes with heating coils or other means to keep the temperature of the water above freezing. This approach is impractical for general use purposes due to the expense of added heating materials and the need for an energy supply to operate the heating coils.

[0004] Another approach to protect pipes from freezing is introducing an antifreeze solution into the water to change the temperature at which water freezes. As an illustration, U.S. Pat. No. 4,664,181 describes a method wherein heating pipes are not filled all the way and a solvent is added to reduce the freezing temperature of the water. In plumbing systems, this practice is usually limited to situations where a system remains dormant for a period of time, such as in a vacation home or on a recreational-use boat. Use of an antifreeze solution generally makes a water supply unusable for human consumption until the pipes are cleared of the solution. In addition, discharge of antifreeze solutions from a plumbing system may be hazardous to the environment.

[0005] Still other means have been attempted in the past to prevent freeze damage to pipes containing water or other liquids. Compressible compartments within branches or reservoirs connected to the outside of water pipes have been used in plumbing systems, such as that described in U.S. Pat. No. 1,672,393. Such systems require extra piping which may not fit in crowded spaces and which adds much extra expense.

[0006] Compressible, air-filled compartments placed within the water flow path inside a pipe are disclosed, for example in U.S. Pat. Nos. 2,409,304, 3,480,027, and 4,649,959. A central compressible core placed inside a pipe containing water is designed to provide an internal expansion volume to accommodate the volume needed when the water freezes. Such internally disposed compressible compartments have a number of disadvantages. For example, the turns, couplings, and other fittings in modern piping do not lend themselves to having a continuous length of compressible core as shown in these patents. Furthermore, the pressure of liquids inside pipes is such that compressible cores might be so compressed that little safety volume would remain for that needed when the water freezes. Moreover, the compressible core may tend to move away from its desired position due to velocity changes of water flowing in the pipe. Additionally, compressible cores add the expense of extra materials and increased installation costs and are subject to stress fatigue and leakage.

[0007] In attempt to overcome disadvantages of air-filled compartments, some pipe freeze protection systems use solid compressible bodies inserted within water pipes, such as described in U.S. Pat. No. 2,360,596. However, these types of insertable bodies are still subject to movement out of position with the flow of water through the pipe. Also, compressible inserts made with rubber and inserts having rubber flanges for holding them in place in the center of the pipe are ineffective. Rubber flanges of adequate size and compressibility cannot be used around bends, such as found near outside faucets where protection is critical and where pipe dimensions vary because of faucets and couplings. As well, rubber deteriorates with age and thus cannot provide permanent freeze protection.

[0008] A different approach to insertable compressible bodies for absorbing expansion of freezing water is disclosed in U.S. Pat. No. 4,773,448. This patent describes a pipe having a rigid outer shell, a smooth flexible inner shell spaced inwardly from the outer shell, and a flexible foam material, such as foamed polyethylene, filling the space between the outer and inner shells. The flexible inner shell is sufficiently elastic to expand the internal volume of the pipe about 10% to accommodate freezing water. A disadvantage of such a design is that the use of two different materials which must be bonded together creates additional manufacturing costs. Operation of such an insert is also plagued with reliability and durability concerns.

[0009] Another system for freeze-protecting an aqueous fluid conduit using a compressible material is disclosed in U.S. Pat. No. 6,119,729. In this system, an elongated compressible elastomeric material is disposed within the conduit along its length. The conduit includes a rigid wall and a substantially liquid impermeable membrane disposed adjacent to the compressible elastomeric material. The conduit may also include rigid structural supports between the membrane and the rigid wall. The compressible elastomeric material, such as silicone foam, foamed butyl rubber, foamed neoprene, silicone sponge rubber, and urethane foam, accommodates expansion caused by freezing. This device is disclosed as particularly suitable for heat transfer applications, such as a solar thermal collector or photovoltaic cells. As noted above, such a system incurs the added expense of materials and manufacturing for separate inner membranes, outer walls, and compressible materials. Furthermore, a flexible fluid-conducting membrane is susceptible to weakening and leakage during prolonged use.

[0010] Rather than rigidly fixing compressible inserts inside the entire length of a pipe, other approaches allow an inner body to move within a pipe. For example, U.S. Pat. No. 4,321,908 discloses an apparatus to prevent freeze damage to a pipe conducting a pressurized liquid by attaching one end of an inner tube to the pipe so as to prevent linear axial movement of the tube and maintaining the other end concentrically within the pipe so as to permit limited linear axial expansion of the tubing inside the pipe. The tube comprises a linear section of tubing which is sealed at each end and contains an inert gas under pressure in excess of the pressure of the liquid in the pipe. When the water begins to freeze and expand, it then compresses the central core. Such a device is unsatisfactory because a continuous length of the compressible core tube does not easily fit within the angles of bends and couplings, fixing the tube in place during installation is complex, the pressurized tube may rupture and thus fail in action, and material and installation costs are excessive.

[0011] U.S. Pat. No. 5,058,627 discloses yet another water pipe anti-rupture system for preventing freeze damage in which a string of hollow cups spaced apart by a common connecting rod are placed within the interior of a pipe such that the cups provide for compression within the pipe. The connecting rod frictionally engages the inside of a water pipe to hold the cups in place substantially in the center and along a length of water pipe with hollows oriented downward so that the cups can entrap air. When water freezes and expands within the pipe, air trapped in the hollow chambers compresses to absorb the expansion of freezing water.

[0012] This type of pipe freeze protection system has several disadvantages. One disadvantage is that the spaced cups must be oriented in a downward direction in order to entrap air, thus requiring different configurations for each length of pipe placed at different angles. For example, for hollows to be oriented downwardly, cups must be oriented one direction in a horizontally-placed pipe and in a different direction in a vertically-placed pipe. Another disadvantage is that to prevent pipe rupture by absorbing expansion of freezing water with air, such a pipe system must entrap a sufficient volume of air to be effective. Yet another disadvantage is that such pipe freeze protection systems are designed for selective use in lengths of pipe in critical areas exposed to freezing, such as from an outside faucet into the interior of a house, rather than along the entire length of a plumbing system.

[0013] In addition, previous approaches to protecting pipes from rupture due to freezing have not addressed in the same design protecting pipes from rupture related to other causes. For example, an increase in temperature and/or pressure of a fluid beyond a pipe's normal elastic limit may not be sufficiently accommodated by air-filled compartments or compressible inserts as in prior designs.

[0014] Until now there has not been a fluid transport or containment system designed to protect such a system from rupture due to an expanding internal volume, particularly rupture due to freezing of fluid, in which the system structure itself is adapted to expand and contract.

[0015] Prior pipe freeze-protection approaches have not combined advantages of a unitary configuration that is sufficiently expandable and contractible to resist rupture during repeated cycles of freezing and thawing with those of a system that allows use of standard-sized pipes with standard pipe fittings, that are economical to manufacture and use, that can be used in virtually any fluid containment and/or fluid transport system, and that overcome disadvantages of systems using separate internal components. It is to these perceived needs that the present invention is directed.

SUMMARY OF THE INVENTION

[0016] The present invention protects fluid transport and containment systems from rupture related to an expanded volume within the systems. In particular, the present invention provides a system for containing and/or transporting fluids having a means for sufficiently expanding when fluids contained therein freeze, thereby resisting freeze-induced rupture.

[0017] In embodiments of the present invention, freeze-damage resistance is provided by pipes having a hollow expansion channel, or relief groove, which runs longitudinally along the pipes. As water inside a pipe freezes and changes from liquid state to a solid ice state, the increase in volume due to such expansion exerts an outward pressure on pipe walls. The pipe walls are able to expand, or move outwardly, in an elastic process, and relieve the stress caused by such volume expansion. In this way, rupture of the pipes can be prevented. Such outward elastic movement of pipe walls in response to expansion caused by freezing fluids is reversible. As such, pipes of the present invention allow pipe walls to contract back, or move inwardly, to substantially their original position when frozen fluid within the pipes thaws. Pipe systems of the present invention include plugs which sealingly fit into each end of the hollow, expansion channels to allow pipes to be utilized in conventional ways including with a variety of fittings, such as elbows, tees, caps, adapters, expanders, reducers, collars, and the like.

[0018] More particularly, embodiments of a fluid transport system resistant to rupture due to expansion of freezing fluid contained within the system as in the present invention include a pipe having an open seam along the length of the pipe and a core structure connected to the inside surface of the pipe along its length. The core structure also has an open seam that is contiguous with the open seam in the pipe wall, and defines a hollow expansion channel along the length of the pipe. The expansion channel has open ends adaptable for sealing with a plug at each end. The pipe and core structure are expandable outwardly in radial fashion from the longitudinal center of the pipe in the direction of the open seams. The pipe wall and core structure of the present invention are expandable, or outwardly moveable, and contractible, or inwardly moveable, so that when fluid contained within the system freezes and expands, the pipe wall and core structure expand, or move outwardly, to accommodate an increased volume, thereby resisting rupture of the system.

[0019] In embodiments, the pipe and the core structure of the present invention comprise an integral pipe unit. The integral pipe unit comprises a configuration having elasticity sufficient to expand greater than an increased volume, for example, the increase in volume caused by freezing of fluid within the pipe system, and to contract to approximately an original non-expanded position, as when frozen fluid within the system thaws.

[0020] In embodiments in which the fluid contained within the pipe system is water, the present invention comprises a pipe and core structure that are sufficiently expandable to accommodate an increased volume of at least 10% when the water freezes.

[0021] Pipes of the present invention can be constructed with any material suitable for transporting fluids that is sufficiently elastic to allow a pipe structure to expand and contract in response to freezing and thawing fluid. Preferably the material is a strong, hard material, such as thermoplastic polymeric materials, including polyvinyl chloride (PVC).

[0022] Embodiments of pipes and pipe systems of the present invention are readily manufactured as the pipe and core structure can be extruded as a single, integral pipe unit. Alternatively, pipes and pipe systems of the present invention can be made by injection molding and by forming a cast of selected material. Preferably, pipe walls and core structures in embodiments of the present invention are made from the same material.

[0023] In preferred embodiments, the pipe, core structure, and plug at each end of the expansion channel comprise a smooth central passageway substantially free of surface irregularities adapted to transport liquid with a minimum of frictional losses.

[0024] Other embodiments of the present invention comprise a fluid container resistant to rupture from an increase in internal volume, for example, from expansion due to freezing of fluid within the container. In such embodiments, a side of the container has an open seam along its length, a core structure connected to the inside surface of the side along its length also having an open seam that is contiguous with the open seam in the side, and a hollow expansion channel, defined by the core structure, along the length of the side.

[0025] Similar to embodiments comprising pipes, in a fluid container of the present invention, the expansion channel has open ends adaptable for sealing with a plug at each end. In other embodiments, fluid containers of the present invention are configured without plugs. The container side and core structure are expandable and contractible so that when fluid contained within the system freezes and expands, the side and core structure expand, or move outwardly, to accommodate an increased volume, thereby resisting rupture of the container. The container side and core structure may further comprise an integral unit having elasticity sufficient to expand outwardly greater than the increased volume caused by freezing of fluid within the container and to contract inwardly to approximately the original non-expanded position when frozen fluid within the container thaws.

[0026] Features of pipes, pipe systems, and containers of the present invention resistant to freeze-induce rupture may be accomplished singularly, or in combination, in one or more of the embodiments of the present invention. As will be appreciated by those of ordinary skill in the art, the present invention has wide utility in a number of applications as illustrated by the variety of features and advantages discussed below.

[0027] For example, the present invention advantageously provides a system resistant to rupture related to freezing of fluids contained within pipes and containers that is effective, reliable, and durable. Embodiments of pipes, pipe systems, and containers of the present invention have a configuration that is sufficiently expandable and contractible to resist rupture during repeated cycles of freezing and thawing.

[0028] Embodiments of the present invention provide advantages over previous approaches to freeze protection of pipes and containers by utilizing a unitary, or integral, structure that overcomes the disadvantages of inserts and compressible compartments positioned within pipes. The present invention avoids the limitations of prior systems using internal components that may become dislodged, rupture during normal use, require precise positioning, limit use of pipes with conventional fittings, and add expense for extra materials and complex installation.

[0029] Pipe systems of the present invention are advantageous in that standard-sized pipes are utilized in conventional ways including with standard pipe fittings such as elbows, tees, caps, collars, adapters, reducers, expanders, and the like.

[0030] Another advantage is that pipes, pipe systems, and containers of the present invention can be constructed with any material suitable for transporting and/or containing fluids that is sufficiently elastic to expand and contract in response to a predetermined increase in internal fluid volume, such as caused by freezing and thawing fluid.

[0031] Another advantage is that embodiments of the present invention can be economically manufactured using currently available equipment and techniques. Pipes of the present invention can be extruded in a single integral unit, and can be made by injection molding. As such, pipes, pipe systems, and containers of the present invention are simple and cost-effective to manufacture, as well as to maintain.

[0032] Still another advantage is that the present invention provides a freeze-rupture resistant system that can be used in virtually any fluid containment and/or fluid transport system in which freezing of the fluid is a risk. For example, pipes and pipe systems of the present invention are useful in new construction and for retrofitting, in domestic and industrial settings, in settings where pipes are likely to be exposed to freezing temperatures and monitoring for freezing is limited, in transportation systems, in water-borne vessels, in fire sprinkler systems, and in agricultural irrigation systems. In addition, the present invention can be used in containers for storing and/or transporting liquids, such as water.

[0033] In addition, the present invention may be advantageously used in pipes and pipe systems susceptible to rupture from causes other than freezing. For example, pipes and pipe systems according to the present invention that contain and/or transport fluids under high-temperature and/or high-pressure conditions would resist rupture due to internal volume expansion from even higher temperatures and/or pressures. Applications in such high-temperature and/or high-pressure conditions avoid the disadvantages of the expense and safety issues of systems using relief valves to prevent pipe rupture.

[0034] As will be realized by those of skill in the art, many different embodiments of a pipe and pipe system resistant to freeze-induced rupture according to the present invention are possible. Additional uses, objects, advantages, and novel features of the invention are set forth in the detailed description that follows and will become more apparent to those skilled in the art upon examination of the following or by practice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0035]FIG. 1 is a diagrammatic view of a cross-section of a pipe used in a pipe stress analysis illustrating a channel cut in the pipe wall and the relative movement of the pipe wall during expansion.

[0036]FIG. 2 is a cut-away view of a diagram illustrating the dimensions of a two inch section of a pipe used in a pipe stress analysis.

[0037]FIG. 3 is a cross-sectional view of a pipe having a core structure defining a relief channel in an embodiment of the present invention.

[0038]FIG. 4 is another cross-sectional view of the pipe in FIG. 3 illustrating the relative movement of the core structure and the pipe wall during expansion in an embodiment of the present invention.

[0039]FIG. 5 is a perspective view of a length of pipe having an integral core structure along the length of the pipe and illustrating a plug for sealing the end of the core structure in an embodiment of the present invention.

[0040]FIG. 6 is a perspective view of the length of pipe in FIG. 5 illustrating the end of the core structure sealed with the plug in an embodiment of the present invention.

[0041]FIG. 7 is a view of an alternative plug for use in embodiments of the present invention.

[0042]FIG. 8 is a perspective view of a fluid container having an integral core structure along the length of the container side and illustrating a plug for sealing the end of the core structure in an embodiment of the present invention.

[0043]FIG. 9 is perspective view of a length of plugs in an embodiment of the present invention.

[0044]FIG. 10 is a perspective view of an embodiment of an adapter for fitting a pipe of the present invention to a conventional circular pipe.

[0045]FIG. 11 includes cross-sectional views of four embodiments of the present invention. FIG. 11A shows an embodiment of a core structure defining one closed expansion channel. FIG. 11B shows an embodiment of a core structure defining two closed expansion channels. FIGS. 11C and 11D show embodiments having more than one core structure.

[0046]FIG. 12 is a cross-sectional view of a pipe having a depression in the pipe wall in an embodiment of the present invention.

DETAILED DESCRIPTION

[0047] The present invention provides a fluid transport system resistant to rupture due to an internal volume expansion. In particular, embodiments of the present invention provide a fluid transport system resistant to rupture due to expansion of freezing fluid contained within the system. Referring to FIGS. 3-6, embodiments of the present invention comprise a pipe 20, having a length 27, and a pipe wall 21. Pipe wall 21 has an inside surface 22 and an outside surface 23 and two adjacent edges 25 along length 27 of the pipe forming an open seam 26. A core structure 30 is connected at area 33 to inside surface 22 of pipe wall 21 along length 27 of the pipe. Core structure 30 has an open seam 31 contiguous with open seam 26 in pipe wall 21. A hollow expansion channel 40 is disposed along length 27 of the pipe and is defined by core structure 30. Expansion channel 40 has ends 41 that are open and adaptable for sealing. Each of the open ends 41 of expansion channel 40 is sealed with a plug 50, shown in FIGS. 5 and 6, to prevent leakage of fluid from pipe lumen 28 during operation. Pipe wall 21 and core structure 30 of the present invention are together expandable and contractible so that when fluid contained within the system freezes and expands, pipe wall 21 and core structure 30 expand outwardly to accommodate an increased volume, thereby resisting rupture of the system.

[0048] In the present invention, embodiments of pipe 20 have a center 29 along length 27 of pipe 20, wherein pipe wall 21 and core structure 30 are expandable outwardly from center 29 of pipe 20 in radial fashion in the direction of open seams 26 and 31. Such outwardly radial forces caused by freezing fluid, for example, cause pipe wall 21 and core structure 30 to expand outwardly and open channel 40 to relieve the attendant pressure.

[0049] In embodiments of the present invention, pipe 20 and core structure 30 comprise an integral pipe unit. The movement of an integral pipe unit due to expansion and contraction, for example from freezing and thawing of fluid, respectively, is shown in FIG. 4, where pipe wall inside surface 22, core structure 30, and channel 40 are shown in an original non-expanded position. The integral pipe unit comprises a configuration having elasticity sufficient to expand greater than the increased volume caused by outwardly expanding forces, such as by freezing of fluid within the system. Thus, when fluid inside pipe 20 freezes, the integral pipe unit expands, or moves outwardly. FIG. 4 shows expanded positions for the pipe wall inside surface at 24, for the core structure at 32, and for the channel at 42. The elasticity modulus is sufficient for the integral pipe unit to contract, or move inwardly, to approximately the original non-expanded position when frozen fluid within the system thaws.

[0050] An optimal configuration for an integral pipe unit according to the present invention was determined by testing and modeling, as described. In the example below, an optimal configuration, or design, has an appropriate size, shape, and placement of core structure 30 relative to pipe wall 21 for adequate movement due to expansion and contraction without rupture as would occur, for example, during repeated cycles of freezing and thawing. As an example, when the fluid contained within the system is water, pipe wall 21 and core structure 30 are configured to be sufficiently expandable and contractible to accommodate an increased volume of at least 10% when the water freezes. Optimal configuration for an integral pipe unit may also change in relation to variables in addition to an expanded volume caused by freezing of a particular fluid inside the pipe. For example, as ambient temperature decreases, such as in outer space or extreme laboratory conditions, pipe materials generally become more brittle, or less flexible. As a consequence, an optimal configuration of an integral pipe unit accommodates not only an internal freeze-induced volume expansion but also less flexibility of pipe material due to lower temperatures.

[0051] As described above, pipe systems of the present invention include plugs 50 which sealingly fit into each end 41 of hollow expansion channels 40 to allow pipes to be utilized in conventional ways including with standard pipe fittings (not shown) such as elbows, tees, caps, collars, expanders, reducers, adapters, and the like.

[0052] Plugs 50 are permanently fixed inside ends 41 of channel 40, and core structure 30, so that the points of contact between plugs 50 and core structure 30 do not move during expansion of fluid against inner surface 22 of pipe wall 21, as during freezing, or during contraction, as with thawing of the frozen mass inside pipe 20. As such, the integrity of the contact between core structure 30 and plugs 50 is maintained, and fluid contained within pipe lumen 28 continues to be contained within pipe lumen 28 during movement of pipe wall 21 related to expansion and contraction. In the present invention, constrained movement related to plugs 50 fixed at both ends 41 of channel 40 is insufficient to restrict expandability, or outward movement, of pipe wall 21 along length 27 of the pipe beyond that necessary to accommodate expansion caused by freezing fluids.

[0053] Pipe systems of the present invention include embodiments of plugs that have elastic compressibility and provide further relief of pipe volume expansion due to freezing of fluids. For example, plugs can be shaped so as to protrude into adjacent fittings, which generally are not flexible, so as to accommodate freeze-induced expansion in fittings. In preferred embodiments, plugs 50 are solid. Alternatively, plugs 50 comprise a hollow core. In other embodiments, pipe systems of the present invention include flexible, tapered plugs 52, as seen in FIG. 7, that are permanently fixed inside ends 41 of channel 40 and core structure 30. Insert portion 54 of plug 52 is inserted into channel 40, allowing taper 53 to extend into a fitting placed on the end of pipe 20. Such flexible, tapered plugs 52 provide a further relief, or cushion, means for expansion, for example, by ice pressing against flexible plug taper 53 such that taper 53 flexes inwardly, thereby allowing more room for freeze-related expansion, particularly in connections between pipes where plugs are located.

[0054] As shown in FIG. 10, pipes of the present invention can be fit to existing, conventional pipes, for example circular pipes, by using an adapter 80. In an embodiment, adapter 80 has a first end 81 and a second end 82 for fitting the pipe to a standard circular pipe 84. First end 81 is larger than pipe 20 for fitting over the end of pipe 20. First end 81 includes an integral plug 50 for sealably contacting end 41 of expansion channel 40. Second end 82 has a circular shape 83 and is further shaped for fitting the end of a circular pipe, for example, in a tapered design, as shown in FIG. 10, to fit inside conventional pipe 84. Alternatively, second end 82 can be designed to fit over the end of standard circular pipe 84 (not shown).

[0055] The present invention comprises a means for efficiently packaging and inserting plugs into the ends of expansion channels. Referring to FIG. 9, in an embodiment, a means 70 for packaging and inserting plugs comprises a series of individual plugs 71 joined from end to end in a length 72 of plugs by a small amount of material 73 between each plug 71 adapted to allow the length of plugs to be easily broken away from an inserted plug. As such, a number of plugs are packaged together in one unit that is conveniently stored and more readily portable for easier insertion of individual plugs into the ends of expansion channels. In operation, a plug at the insertion end 74 in length 72 of breakaway plugs is inserted into end 41 of expansion channel 40 (as seen in FIG. 5). After plug 75 is inserted into end 41 of channel 40, length 77 of breakaway plugs is then bent by the operator so as to break length 77 of plugs away from plug 75 at breakaway point 76 adjacent plug 75. The insertion and break away steps are repeated to sequentially place plugs at the insertion end in a length of breakaway plugs into the ends of expansion channels. In this manner, an operator can more easily and quickly insert plugs into expansion channels and avoid unnecessary contact with adhesives used to secure the plugs in place. Embodiments of a length of breakaway plugs according to the present invention comprise plugs sized to fit various sizes of expansion channels.

[0056] In other embodiments, pipes of the present invention comprise configurations having one or more expansion channels that are closed, rather than “hollow,” as described above. For example, as shown in FIG. 11, a core structure 30 may define one closed expansion channel 90 (FIG. 11A), as well as two closed expansion channels 90 (FIG. 11B). Embodiments having closed expansion channels operate without the use of plugs. Moreover, embodiments of the present invention comprise more than one core structure 30, as seen in FIGS. 11C and 11D.

[0057] In other embodiments of the present invention, a fluid transport system resistant to rupture due to expansion of the internal fluid volume, as seen in FIG. 12, comprises a pipe 20 having at least one depression 91 in pipe wall 21 toward the cross-sectional center 29 of the pipe 20 and along the length of the pipe. Each of the one or more longitudinal depressions 91 defines an external expansion channel 40. Such an embodiment is designed so that pipe wall 21 is expandable outwardly from the center 29 of the pipe in the direction of the one or more depressions 91. When the internal fluid volume expands, pipe wall 21 expands sufficiently to accommodate the expanded volume and resist rupture of the system. For example, when the internal fluid volume expands due to freezing of fluid inside pipe 20, pipe wall 21 is sufficiently elastic to expand outwardly greater than the expanded internal fluid volume caused by the freezing and to contract to approximately an original non-expanded position when the frozen fluid thaws. In particular, when the internal fluid is water, the pipe wall in such embodiments is sufficiently expandable to accommodate an expanded volume of at least 10% when the water freezes.

[0058] Pipes, pipe systems, and fluid containers of the present invention can be constructed with any material suitable for transporting and/or containing fluids that is configured to be sufficiently elastic to expand outwardly in response to a particular increase in internal volume, such as caused by freezing, and contract inwardly when the volume decreases, as with thawing. Preferably the material is a strong, hard material, such as thermoplastic polymeric materials. Most preferably, pipes and containers of the present invention are made from polyvinyl chloride (PVC). Pipes, pipe systems, and containers of the present invention made from PVC and PVC composites are advantageous as compared to copper and other like materials because PVC and PVC composites are less expensive and are more resistant to damage and leaking. Other embodiments comprise pipes and containers made from ABS copolymers, composites, and other like materials.

[0059] In preferred embodiments, pipe 20, core structure 30, and plugs 50 at each end of expansion channel 40 comprise a smooth central passageway substantially free of surface irregularities adapted to transport liquid with a minimum of frictional losses. In embodiments, a core structure and expansion channel can have configurations other than the typical circular pipe shape. Embodiments of pipes of the present invention have a capacity to transport a volume of fluid that is less than a pipe of the same inside diameter without a core structure, but the decrease in volume capacity is insignificant. As an optional compensation for a decreased capacity in volume due to the presence of a core structure, fluid pressure may be increased slightly. Alternatively, a pipe as in the present invention can be manufactured in larger than standard sizes to compensate for any loss of volume capacity due to presence of a core structure.

[0060] Embodiments of pipes and pipe systems of the present invention are readily manufactured, as pipe 20 and core structure 30 can be extruded as a single, integral pipe unit. Preferably, pipe walls 21 and core structures 30 in embodiments of the present invention are made from the same material. In an alternative manufacturing approach, pipes and pipe systems of the present invention can be made by injection molding. In addition, pipes and pipe systems of the present invention can be made by forming a cast of the material, as well as by other methods suitable for forming an integral pipe unit. As such, embodiments of the present invention can be economically manufactured using currently available equipment and techniques.

[0061] As illustrated in FIG. 8, other embodiments of the present invention include a fluid container 60 resistant to rupture due to an expanded internal volume, such as caused by freezing of fluid within the container, in which a side 61 of container 60 has an open seam 62 along its length 63 and a core structure 64 connected to the inside surface of side 61 along its length 63. Core structure 64 also has an open seam (not shown) that is contiguous with open seam 62 in side 61, and a hollow expansion channel 65, defined by core structure 64, along length 63 of side 61.

[0062] As shown in FIG. 8, in embodiments of fluid containers of the present invention, expansion channel 65 has open ends 66 adaptable for sealing with a plug 67 at each end 66. Plugs 67 may be hollow; however, plugs 67 are preferably solid. Container side 61 and core structure 64 are outwardly expandable and inwardly contractible so that when fluid contained within the system freezes and expands, side 61 and core structure 64 expand to accommodate an increased volume, thereby resisting rupture of the container. Container side 61 and core structure 64 may further comprise an integral unit having elasticity sufficient to expand greater than the increased volume caused by freezing of fluid within container 60 and to contract to approximately the original non-expanded position when frozen fluid within container 60 thaws. In preferred embodiments of fluid containers, core structure 64 and container top 68 comprise an integral unit such that fluids are contained within container 60, and plugs are not used.

[0063] Similar to pipes and pipe systems described above, embodiments of fluid containers of the present invention can be manufactured from thermoplastic polymeric materials, such as polyvinyl chloride, and comprise extruded material, injection molded material, and/or a cast of material.

[0064] As mentioned above, the pipe and pipe system of the present invention that provide protection against rupture, such as caused by freezing, have numerous applications. For example, freeze-rupture resistant pipes of the present invention can be used in domestic and industrial settings, both in new construction and for retrofitting in existing plumbing systems. Such pipes and pipe systems can readily be used in mobile homes and pre-manufactured buildings, which often have less insulation than conventional-built structures. Freeze-protected pipes of the present invention are particularly useful in settings where pipes are likely to be exposed to freezing temperatures and monitoring for freezing is limited, such as in a vacation home of a non-resident owner. Other applications for freeze-rupture resistant pipes of the present invention in which monitoring for freezing may be limited is in motor homes, campers, and recreational vehicles. The present invention can be used in plumbing of transportation systems, including airplanes, trains, buses, and ferries, as well as in other water-borne vessels such as ships, yachts, and houseboats. Pipes of the present invention, resistant to freeze rupture, are especially beneficial in dedicated, special purpose fluid transport systems in which integrity and patency of the system is critical for safety and/or catastrophe prevention. Special purpose fluid transport systems that can benefit from such pipes include, for example, fire sprinkler systems, particularly self-draining fire sprinkler systems, and irrigations systems in nurseries, farming, and agriculture. In addition, embodiments of the present invention can be used in other plumbing applications, such as in liquid effluent drains.

[0065] In addition, the present invention provides a system that resists freeze-induced rupture that can be used in fluid containment and/or fluid transport applications other than plumbing. For example, embodiments of the present invention could provide freeze-rupture resistance to containers used to store and/or transport potable liquids, such as water. Another application of the present invention is in containers used to store and/or transport liquids having a freezing point near the temperature range of a working environment, such as in extreme temperature laboratory conditions and in space vehicles. A freeze-rupture resistant system of the present invention could be used in virtually any fluid containment and/or fluid transport situation in which freezing of the fluid is a risk.

[0066] Moreover, pipes, pipe systems, and containers of the present invention resist rupture from causes other than freezing. For example, pipes, pipe systems, and containers according to the present invention that contain and/or transport fluids under high-temperature and/or high-pressure conditions resist rupture due to internal volume expansion from even higher temperatures and/or pressures.

[0067] In embodiments of the present invention, a fluid transport system, having an internal volume, resistant to rupture due to expansion of the internal volume comprises: a pipe having a length and a pipe wall, the pipe wall having an inside surface and an outside surface and two adjacent edges along the length of the pipe forming an open seam; a core structure connected to the inside surface of the pipe wall along the length of the pipe and having an open seam contiguous with the open seam in the pipe wall; and a hollow expansion channel along the length of the pipe defined by the core structure, wherein the pipe has a center along the length of the pipe and the pipe wall and the core structure are expandable outwardly from the center of the pipe in the direction of the open seams, and wherein when the internal volume expands, the pipe wall and core structure expand sufficiently to accommodate the expanded volume and resist rupture of the system.

[0068] In embodiments of a fluid transport system of the present invention, the pipe and the core structure comprise an integral pipe unit. In such a fluid transport system, the integral pipe unit has an original non-expanded position, and the expanded internal volume is caused by freezing of fluid inside the pipe, wherein the integral pipe unit comprises a configuration having elasticity sufficient to expand outwardly greater than the expanded internal volume caused by the freezing of the fluid and to contract to approximately the original non-expanded position when the frozen fluid thaws. In embodiments wherein the fluid inside the pipe is water, the integral pipe unit is sufficiently expandable to accommodate an expanded volume of at least 10% when the water freezes.

[0069] A fluid transport system of the present invention can have a hollow expansion channel having open ends adaptable for sealing, wherein the system further comprises a plug sealably contacting each end of the expansion channel. In embodiments, such plugs are solid. Alternatively, embodiments of such plugs are hollow.

[0070] In embodiments of a fluid transport system of the present invention, the pipe is connectable to another pipe with pipe fittings each having an internal volume, wherein the plug has a portion for inserting into the end of the expansion channel and a compressible portion for protruding into adjacent pipe fittings so that when the volume in the pipe fittings expands, the compressible portion compresses to accommodate the expanded volume and resist rupture of the system. The compressible portion of the plug for protruding into adjacent pipe fittings can be tapered.

[0071] In embodiments, the fluid transport system further comprises an adapter for fitting the pipe to a conventional pipe, the adapter having a first end comprising a shape adapted to form a sealable fit with the pipe and a second end comprising a shape adapted to form a sealable fit with the conventional pipe. In other embodiments, the pipe has an end, wherein the first end of the adapter comprises an integral plug for sealably contacting the end of the expansion channel and wherein the first end of the adapter is larger than the pipe for sealably fitting over the end of the pipe. In still other embodiments, the pipe is connectable to another pipe with pipe fittings, wherein the second end of the adapter comprises a shape adapted to form a sealable fit with the pipe fittings, the second end further comprising a compressible portion for protruding into adjacent pipe fittings so that when the volume in the pipe fittings expands, the compressible portion compresses to accommodate the expanded volume and resist rupture of the system.

[0072] In the present invention, embodiments of a fluid transport system include a pipe and a core structure that comprise a thermoplastic material. The thermoplastic material may be polyvinyl chloride. In other embodiments, the pipe and the core structure comprise a metallic material.

[0073] Embodiments of the fluid transport system of the present invention include a pipe and a core structure that comprise a unitarily extruded material. In other embodiments, the pipe and the core structure comprise an injection molded material.

[0074] In embodiments of a fluid transport system of the present invention, the pipe, the core structure, and the plug at each end of the expansion channel comprise a smooth central passageway substantially free of surface irregularities adapted to transport liquid with a minimum of frictional losses.

[0075] In the present invention, a fluid transport system comprises a plurality of plugs, further comprising a means for packaging the plurality of plugs and inserting one of the packaged plurality of plugs into each end of the expansion channel. Embodiments of the means for packaging and inserting plugs comprise a first length of the plurality of plugs having each of the plurality of plugs connected sequentially end to end by material adaptable for breaking, wherein a plug at the end of the first length of plugs is inserted into the end of the expansion channel and the inserted plug is broken away from the first length of plugs at the connecting material to provide a second length of plugs ready for repeating the insertion and breaking away steps.

[0076] In embodiments of the present invention, the fluid transport system is a plumbing system. In other embodiments, the fluid transport system is a fire sprinkler system. In still other embodiments, the fluid transport system is an irrigation system.

[0077] In embodiments of the present invention, a fluid transport system, having an internal volume, resistant to rupture due to expansion of the internal volume, comprises: a pipe having a length and a pipe wall, the pipe wall having an inside surface and an outside surface and two adjacent edges along the length of the pipe forming an open seam; a core structure connected to the inside surface of the pipe wall along the length of the pipe and having an open seam contiguous with the open seam in the pipe wall; and a hollow expansion channel along the length of the pipe defined by the core structure, wherein the pipe and the core structure comprise an integral pipe unit, wherein the pipe has a center along the length of the pipe and the integral pipe unit is expandable outwardly from the center of the pipe in the direction of the open seams, and wherein when the internal volume expands, the integral pipe unit expands sufficiently to accommodate the expanded volume and resist rupture of the system.

[0078] In embodiments wherein the pipe and the core structure comprise an integral pipe unit, the hollow expansion channel has open ends adaptable for sealing, and the system further comprises a plug sealably contacting each end of the expansion channel. In such embodiments of the present invention, the plug is solid. Alternatively, embodiments of such plugs are hollow.

[0079] In a embodiments of a fluid transport system of the present invention wherein the pipe and the core structure comprise an integral pipe unit, the pipe is connectable to another pipe with pipe fittings, wherein the plug has a portion for inserting into the end of the expansion channel and a compressible portion for protruding into adjacent pipe fittings so that when the volume in the pipe fittings expands, the compressible portion compresses to accommodate the expanded volume and resist rupture of the system. The compressible portion of the plug for protruding into adjacent pipe fittings can be tapered.

[0080] In embodiments wherein the pipe and the core structure comprise an integral pipe unit, the fluid transport system further comprises an adapter for fitting the pipe to a conventional pipe, the adapter having a first end comprising a shape adapted to form a sealable fit with the pipe and a second end comprising a shape adapted to form a sealable fit with the conventional pipe. In embodiments, the pipe has an end, wherein the first end of the adapter comprises an integral plug for sealably contacting the end of the expansion channel and wherein the first end of the adapter is larger than the pipe for sealably fitting over the end of the pipe. In other embodiments wherein the pipe and the core structure comprise an integral pipe unit, the pipe is connectable to another pipe with pipe fittings each having an internal volume, wherein the second end of the adapter comprises a shape adapted to form a sealable fit with the pipe fittings, the second end further comprising a compressible portion for protruding into adjacent pipe fittings so that when the volume in the pipe fittings expands, the compressible portion compresses to accommodate the expanded volume and resist rupture of the system.

[0081] In the present invention wherein the pipe and the core structure comprise an integral pipe unit, embodiments the integral pipe unit comprise a thermoplastic material. The thermoplastic material may be polyvinyl chloride. In other embodiments wherein the pipe and the core structure comprise an integral pipe unit, the integral pipe unit comprises a metallic material.

[0082] Embodiments of an integral pipe unit of the present invention comprise an extruded material. In other embodiments, the integral pipe unit comprises an injection molded material.

[0083] In embodiments of a fluid transport system of the present invention, the integral pipe unit and the plug at each end of the expansion channel comprise a smooth central passageway substantially free of surface irregularities adapted to transport liquid with a minimum of frictional losses.

[0084] In the present invention wherein the pipe and the core structure comprise an integral pipe unit, a fluid transport system comprises a plurality of plugs, further comprising a means for packaging the plurality of plugs and inserting one of the packaged plurality of plugs into each end of the expansion channel. Embodiments of the means for packaging and inserting plugs comprise a first length of the plurality of plugs having each of the plurality of plugs connected sequentially end to end by material adaptable for breaking, wherein a plug at the end of the first length of plugs is inserted into the end of the expansion channel and the inserted plug is broken away from the first length of plugs at the connecting material to provide a second length of plugs ready for repeating the insertion and breaking away steps.

[0085] In embodiments of the present invention, the fluid transport system comprising an integral pipe unit is a plumbing system. In other embodiments, the fluid transport system comprising an integral pipe unit is a fire sprinkler system. In still other embodiments, the fluid transport system comprising an integral pipe unit is an irrigation system.

[0086] In embodiments of the present invention, a fluid container, having an internal volume, resistant to rupture due to expansion of the internal volume, comprises: a plurality of sides, one of the plurality of sides having a length and an inside surface and two adjacent edges along the length of the one side forming an open seam; a core structure connected to the inside surface and along the length of the one side and having an open seam contiguous with the open seam in the one side; and a hollow expansion channel along the length of the one side defined by the core structure, wherein the one side and the core structure comprise an integral unit, wherein the integral unit is expandable outwardly in the direction of the open seams, and wherein when the internal volume expands, the integral unit expands sufficiently to accommodate the expanded volume and resist rupture of the system.

[0087] In embodiments of the fluid container of the present invention, the integral unit has an original non-expanded position, and the expanded internal volume is caused by freezing of fluid inside the container, wherein the integral unit comprises a configuration having elasticity sufficient to expand outwardly greater than the expanded internal volume caused by the freezing of the fluid and to contract to approximately the original non-expanded position when the frozen fluid thaws. In embodiments wherein the fluid inside the container is water, the integral unit is sufficiently expandable to accommodate an expanded volume of at least 10% when the water freezes.

[0088] A fluid transport system of the present invention can have a hollow expansion channel having open ends adaptable for sealing, the container further comprising a plug sealably contacting each end of the expansion channel. In embodiments, the plug is solid. In other embodiments, the plug is hollow.

[0089] In the present invention, embodiments of an container comprise a thermoplastic material. The thermoplastic material may be polyvinyl chloride. In other embodiments, the container comprises a metallic material.

[0090] Embodiments of a container of the present invention comprise an extruded material. In other embodiments, the container comprises an injection molded material.

[0091] In embodiments of the present invention, a fluid transport system, having an internal volume, resistant to rupture due to expansion of the internal volume, comprise a pipe having a length and a pipe wall, the pipe having a center along the length of the pipe, the pipe wall comprising at least one depression toward the center and along the length of the pipe, each of the at least one depression defining an external expansion channel, wherein the pipe wall is expandable outwardly from the center of the pipe in the direction of the at least one depression, and wherein when the internal volume expands, the pipe wall expands sufficiently to accommodate the expanded volume and resist rupture of the system.

[0092] In embodiments of the present invention wherein the pipe wall comprises at least one depression, the pipe wall has an original non-expanded position, and the expanded internal volume is caused by freezing of fluid inside the system, wherein the pipe wall comprises a configuration having elasticity sufficient to expand outwardly greater than the expanded internal volume caused by the freezing of the fluid and to contract to approximately the original non-expanded position when the frozen fluid thaws. In embodiments wherein the pipe wall comprises at least one depression and wherein the fluid inside the system is water, the pipe wall is sufficiently expandable to accommodate an expanded volume of at least 10% when the water freezes.

[0093] In embodiments wherein the pipe wall comprises at least one depression, the fluid transport system further comprises an adapter for fitting the pipe to a conventional pipe, the adapter having a first end comprising a shape adapted to form a sealable fit with the pipe and a second end comprising a shape adapted to form a sealable fit with the conventional pipe. In embodiments of a fluid transport system of the present invention wherein the pipe wall comprises at least one depression, the pipe has an end, wherein the first end of the adapter comprises an integral plug for sealably contacting the end of the expansion channel and wherein the first end of the adapter is larger than the pipe for sealably fitting over the end of the pipe. In other embodiments wherein the pipe wall comprises at least one depression, the pipe is connectable to another pipe with pipe fittings, wherein the second end of the adapter comprises a shape adapted to form a sealable fit with the pipe fittings, the second end further comprising a compressible portion for protruding into adjacent pipe fittings so that when the volume in the pipe fittings expands, the compressible portion compresses to accommodate the expanded volume and resist rupture of the system.

EXAMPLE

[0094] This example is set forth by way of illustration and is not intended to limit the scope of the invention. As described above, material testing and experimental modeling were conducted to determine at least one configuration for pipes having an expandable channel to provide structural relief and thus resistance to rupture, as, in this instance, when water contained within the pipes freezes. One objective of such testing and modeling is to determine configuration(s) that are optimal for resistance to pipe rupture related to expansion of internal pipe volume. In this example of determining appropriate pipe configurations in embodiments of the present invention, stress analysis was performed for polyvinyl chloride (PVC), which was assumed to be linearly elastic over the range of pressures considered. Results of the stress analysis were then utilized in design optimization modeling considering a single standard cylindrical piping size. Such stress analysis and design optimization methodology can be applied to pipes of various sizes and materials.

[0095] First, wall stress analysis was conducted for PVC pipe according to standard design specifications for PVC pipe provided by the American Society for Testing of Materials (ASTM specification D1785-85). For example, types 1120, 1220, 4116, 2112, 2116, and 2120 of a standard one inch nominal size PVC pipe have the wall thickness, diameter, weight, and bursting pressures given by ASTM as listed in Table 1 below. See, Marks' Standard Handbook for Mechanical Engineers, Ninth Edition, pages 8-198. TABLE 1 ASTM Specifications of Commercial Size PVC Pipe Nominal Size (inches) 1.0 Schedule 40 Wall thickness (inches) 0.113 OD (inches) 1.315 ID (inches) 1.049 Theoretical weight (lb/ft) 0.305 Calculated min. bursting pressure (lb/in²): 1,440 PVC 1120, 1220, 4116 Calculated min. bursting pressure (lb/in²): 1,130 PVC 2112, 2116, 2120

[0096] The fundamental equation for calculation of circumferential or tangential stress in a thick-walled cylindrical vessel is given as

σ_(t) =p _(i)(b ² +a ²)/(b ² +a ²),

[0097] where σ_(t) is the tangential stress at the inner surface, p_(i) is the internal pressure, and a and b are the inner and outer radii, respectively. In this analysis, a 2% safety margin beyond the elastic limit for the known value of tensile stress of rigid PVC is given as 6,000 psi. Using minimum burst pressure values and the known tensile strength of PVC, it is possible to model new designs for PVC pipe with similar factors of safety.

[0098] As water freezes in pipes, it expands the pipe walls orthogonally, i.e., at right angles, or outwardly in radial fashion, producing an anisotropic stress. Referring to the cross-section in FIG. 1, when a circular pipe, such as test pipe 10, has a seam 14, or relief channel, along its length, and water freezes inside the pipe, pipe wall 11 reshapes to force open seam 14 to accommodate expansion caused by freezing. In FIG. 1, the inside surface of pipe wall 11 is shown in its normal, unexpanded position 12, and in expanded position 13. Outward movement of pipe wall 11 during expansion causes seam 14 to move from its normal, unexpanded position 15 to an expanded position 16. Because elastic modulus is a function of temperature, this elastic process is reversible when temperature increases. Thus, as temperature rises and ice inside pipe 10 thaws, pipe wall 11 moves from expanded position 13 toward its normal, pre-expansion position 12. Inward movement of pipe wall 11 during contraction causes seam 14 to move from expanded position 16 to its normal, pre-expansion position 15.

[0099] Since test pipe 10 has a seam 14 and is therefore movable in response to freeze-induced expansion, pipe wall 11 experiences different stresses than a pipe without a seam. Instead of the typical uniform tangential stresses in a closed circular cross-section, bending stress is formed in a region of the pipe wall 17 diametrically opposite seam 14. As such, analysis of pipe wall stresses in test pipe 10 include calculations for deformation caused by bending. Bending stress is calculated from such deformation using a flexure formula, taking into consideration an otherwise symmetrical structure. (Calculations for a curved beam may also be used.) It is known that when water freezes, its volume expands 9%. As a margin of safety, this analysis considers the amount of cross-sectional deformation required for a 10% volume expansion.

[0100] As an example, pipe wall stress analysis was performed on a section of one inch nominal size, schedule 40, commercial PVC pipe, according to the specifications in Table 1. FIGS. 2A and 2B show cut-away views of a diagram illustrating the dimensions, listed in Table 2, of a two inch section of the pipe used in the following analysis. TABLE 2 Test Pipe Section Dimensions Inside Radius (a) 0.5245 inches Outside Radius (b) 0.6575 inches Length (1)   2.0 inches Angle θ 70°

[0101] (1) Lateral deflection: Lateral deflection at the free end of pipe section 10 necessary to increase the volume of the section by 10% is next determined. Since results of this stress analysis will be used to design an optimal configuration for radial expansion of a pipe, determination of lateral deflection (and volume increase) assumes that volume expansion will cause an increase in the cross-sectional area only and not in the axial length. Increase in cross-sectional area correlates to an increase in the radius of curvature.

[0102] Luminal area of the pipe section is calculated as:

A _(initial)=¼Πa ²+(0.1944)Πa ²(0.444)=0.3841 in².

[0103] The volume of water contained within the two inch section of the pipe after 10% expansion is approximated as:

V _(final) =Πa ² (0.444)(1)=Π(0.5245)²(0.444)(2.0)=0.7675 in³.

[0104] Solving for the new radius of curvature after 10% expansion gives:

A=[V /Π(2.01)]^(½)=[(0.7675 in³)/Π(2.01)]^(½)=0.5504 in.

[0105] Finally, lateral deflection of the end of pipe 10 caused by 10% volumetric expansion is determined by subtracting the old radius of curvature from the new radius of curvature to give: 0.5504−0.4225=0.1279 in.

[0106] (2) Maximum load to cause deflection: Next, the maximum load required to create this deflection of the free end of pipe section 10 is determined using the lateral deflection calculated above. The cross-sectional moment of inertia (I) must first be determined, as follows:

I={fraction (1/12 )}bh ³ ={fraction (1/12)}(2.0)(0.6575−0.5245)³=3.92×10⁻⁴ in⁴.

[0107] Deflection for cantilever beams is calculated using the formula:

v=P1³/3EI,

[0108] where v is lateral deflection, P is applied load, and E is elastic modulus.

[0109] At room temperature, the elastic modulus for rigid PVC is 400,000 psi, and at −20° F. the modulus increases to approximately 450,000 psi. Using the cold temperature stiffness for the present calculation, with all variables known except P, the maximum load required to create the lateral deflection caused by 10% volumetric expansion is:

P=3EIv/1³=3(450,000)(3.92×10⁻⁴)(0.1279)/(1.0174)³=64.27 pounds.

[0110] (3) Maximum bending stress: The maximum bending stress in pipe section 10 (a beam) is then determined using the flexure formula to give:

σ=My/I=Ply/I=(57.14)(0.0665)(3.92×10⁻⁴)=10,903 psi.

[0111] (4) Comparison of maximum bending stress to tensile strength: The tensile strength of high-impact rigid PVC is known to be

[0112]6,000 psi at room temperature and approximately 9,500 psi at −20° F. Medium-impact rigid PVCs have tensile strengths given in a range between 10,000 and 11,500 psi. See, L. I. Nass, Encyclopedia of PVC, volume 3, chapter 30.

[0113] The lower tensile strength value at −20° F. is compared to the maximum bending stress due to a 10% volumetric expansion in test pipe section 10. This comparison (9,500 psi/10,903 psi=87%) indicates that the maximum bending stress when water freezes in test pipe 10 exceeds the pipe tensile strength at −20° F. by 13%. Therefore, a design configuration for the pipe used in this analysis must accommodate a cross-sectional expansion of approximately 13% to allow for expansion of freezing water and avoid freeze-induced rupture.

[0114] (5) Design modeling: Results of the pipe wall stress analysis were then used to perform computer-assisted geometric and finite element modeling of pipe designs that would accommodate such an expansion. Models employed symmetry about longitudinal midline 18 of pipe 10. The pipe wall region 17 diametrically opposite seam 14, or relief channel, was held in a rigidly fixed position, while nodes in the middle half-plane of the pipe were allowed to move only in the direction toward the relief channel. Pressure was applied to the inside lumen surface 12. In all cases, enough pressure was applied so as to create a deflection consistent with the previously determined bending calculations. The elastic modulus was selected to be 450,000 psi and the tensile strength was selected to be 9,500 psi. Both figures are conservative, as elastic modulus may be as high as 480,000 psi and tensile strength may be as high as 11,500 psi.

[0115] The Rankine failure criteria was used in which maximum principal stress was compared to the known tensile strength of the material at −20° F. After several iterations, a design was found which supported a 40,000 psi load, which is 20 times greater than the published minimal burst pressure for a commercial, one-inch nominal size PVC pipe at room temperature. For this cross-section, a 40,000 psi load imparts a bending stress to the pipe that is at or near the elastic limit for PVC at −20° F.

[0116] Stress analysis and modeling experiments, such as those described above, can be similarly applied to other sizes of pipes of various materials to achieve design optimization objectives. Optimal configuration for an integral pipe unit as in the present invention also relates to variables in addition to a volume of expansion caused by freezing of a particular fluid inside the pipe, such as decreased pipe material flexibility due to decreased ambient temperatures.

[0117] (6) Empirical testing: Although the numerical model predicted some regions of stress slightly above the published tensile strength of rigid PVC, freeze-thaw experiments with a similar cross-section of pipe showed the integral pipe structure expanded outwardly during freezing and contracted inwardly during thawing in reliable fashion. After repeated cycles of freezing and thawing, there was no permanent plastic deformation or bursting. Thus, under freeze-thaw conditions as in actual use, pipes according to the present invention do not rupture as would ordinary pipes under similar conditions. Consequently, such a pipe configuration is useful in embodiments of the present invention to resist freeze-induced rupture.

[0118] Although the present invention has been described with reference to particular embodiments, it should be recognized that these embodiments are merely illustrative of the principles of the present invention. Those of ordinary skill in the art will appreciate that the pipes, pipe systems, and containers of the present invention may be constructed and implemented in other ways and embodiments. Accordingly, the description herein should not be read as limiting the present invention, as other embodiments also fall within the scope of the present invention. 

What is claimed is:
 1. A fluid transport system having an internal volume, the system resistant to rupture due to expansion of the internal volume, comprising: a pipe having a length and a pipe wall, the pipe wall having an inside surface and an outside surface and two adjacent edges along the length of the pipe forming an open seam; a core structure connected to the inside surface of the pipe wall along the length of the pipe and having an open seam contiguous with the open seam in the pipe wall; and a hollow expansion channel along the length of the pipe defined by the core structure, wherein the pipe has a center along the length of the pipe and the pipe wall and the core structure are expandable outwardly from the center of the pipe in the direction of the open seams, and wherein when the internal volume expands, the pipe wall and core structure expand sufficiently to accommodate the expanded volume and resist rupture of the system.
 2. The fluid transport system of claim 1, wherein the pipe and the core structure comprise an integral pipe unit.
 3. The fluid transport system of claim 2, the integral pipe unit having an original non-expanded position, and the expanded internal volume is caused by freezing of fluid inside the pipe, wherein the integral pipe unit comprises a configuration having elasticity sufficient to expand outwardly greater than the expanded internal volume caused by the freezing of the fluid and to contract to approximately the original non-expanded position when the frozen fluid thaws.
 4. The fluid transport system of claim 3, wherein the fluid inside the pipe is water and the integral pipe unit is sufficiently expandable to accommodate an expanded volume of at least 10% when the water freezes.
 5. The fluid transport system of claim 1, the hollow expansion channel having open ends adaptable for sealing, the system further comprising a plug sealably contacting each end of the expansion channel.
 6. The fluid transport system of claim 5, wherein the plug is solid.
 7. The fluid transport system of claim 5, wherein the plug is hollow.
 8. The fluid transport system of claim 5, the pipe being connectable to another pipe with pipe fittings each having an internal volume, wherein the plug has a portion for inserting into the end of the expansion channel and a compressible portion for protruding into adjacent pipe fittings so that when the volume in the pipe fittings expands, the compressible portion compresses to accommodate the expanded volume and resist rupture of the system.
 9. The fluid transport system of claim 8, wherein the compressible portion of the plug for protruding into adjacent pipe fittings is tapered.
 10. The fluid transport system of claim 5, the system further comprising an adapter for fitting the pipe to a conventional pipe, the adapter having a first end comprising a shape adapted to form a sealable fit with the pipe and a second end comprising a shape adapted to form a sealable fit with the conventional pipe.
 11. The fluid transport system of claim 10, the pipe having an end, wherein the first end of the adapter comprises an integral plug for sealably contacting the end of the expansion channel and wherein the first end of the adapter is larger than the pipe for sealably fitting over the end of the pipe.
 12. The fluid transport system of claim 10, the pipe being connectable to another pipe with pipe fittings, wherein the second end of the adapter comprises a shape adapted to form a sealable fit with the pipe fittings, the second end further comprising a compressible portion for protruding into adjacent pipe fittings so that when the volume in the pipe fittings expands, the compressible portion compresses to accommodate the expanded volume and resist rupture of the system.
 13. The fluid transport system of claim 1, wherein the pipe and the core structure comprise a thermoplastic material.
 14. The fluid transport system of claim 13, wherein the thermoplastic material is polyvinyl chloride.
 15. The fluid transport system of claim 1, wherein the pipe and the core structure comprise a metallic material.
 16. The fluid transport system of claim 1, wherein the pipe and the core structure comprise a unitarily extruded material.
 17. The fluid transport system of claim 1, wherein the pipe and the core structure comprise an injection molded material.
 18. The fluid transport system of claim 1, wherein the pipe, the core structure, and the plug at each end of the expansion channel comprise a smooth central passageway substantially free of surface irregularities adapted to transport liquid with a minimum of frictional losses.
 19. The fluid transport system of claim 5, wherein the system comprises a plurality of the plugs, further comprising a means for packaging the plurality of plugs and inserting one of the packaged plurality of plugs into each end of the expansion channel.
 20. The fluid transport system of claim 19, wherein the means for packaging and inserting plugs comprises a first length of the plurality of plugs having each of the plurality of plugs connected sequentially end to end by material adaptable for breaking, wherein a plug at the end of the first length of plugs is inserted into the end of the expansion channel and the inserted plug is broken away from the first length of plugs at the connecting material to provide a second length of plugs ready for repeating the insertion and breaking away steps.
 21. The fluid transport system of claim 1, wherein the fluid transport system is a plumbing system.
 22. The fluid transport system of claim 1, wherein the fluid transport system is a fire sprinkler system.
 23. The fluid transport system of claim 1, wherein the fluid transport system is an irrigation system.
 24. A fluid transport system having an internal volume, the system resistant to rupture due to expansion of the internal volume, comprising: a pipe having a length and a pipe wall, the pipe wall having an inside surface and an outside surface and two adjacent edges along the length of the pipe forming an open seam; a core structure connected to the inside surface of the pipe wall along the length of the pipe and having an open seam contiguous with the open seam in the pipe wall; and a hollow expansion channel along the length of the pipe defined by the core structure, wherein the pipe and the core structure comprise an integral pipe unit, wherein the pipe has a center along the length of the pipe and the integral pipe unit is expandable outwardly from the center of the pipe in the direction of the open seams, and wherein when the internal volume expands, the integral pipe unit expands sufficiently to accommodate the expanded volume and resist rupture of the system.
 25. The fluid transport system of claim 24, the hollow expansion channel having open ends adaptable for sealing, the system further comprising a plug sealably contacting each end of the expansion channel.
 26. The fluid transport system of claim 25, wherein the plug is solid.
 27. The fluid transport system of claim 25, wherein the plug is hollow.
 28. The fluid transport system of claim 25, the pipe being connectable to another pipe with pipe fittings, wherein the plug has a portion for inserting into the end of the expansion channel and a compressible portion for protruding into adjacent pipe fittings so that when the volume in the pipe fittings expands, the compressible portion compresses to accommodate the expanded volume and resist rupture of the system.
 29. The fluid transport system of claim 28, wherein the compressible portion of the plug for protruding into adjacent pipe fittings is tapered.
 30. The fluid transport system of claim 25, the system further comprising an adapter for fitting the pipe to a conventional pipe, the adapter having a first end comprising a shape adapted to form a sealable fit with the pipe and a second end comprising a shape adapted to form a sealable fit with the conventional pipe.
 31. The fluid transport system of claim 30, the pipe having an end, wherein the first end of the adapter comprises an integral plug for sealably contacting the end of the expansion channel and wherein the first end of the adapter is larger than the pipe for sealably fitting over the end of the pipe.
 32. The fluid transport system of claim 30, the pipe being connectable to another pipe with pipe fittings each having an internal volume, wherein the second end of the adapter comprises a shape adapted to form a sealable fit with the pipe fittings, the second end further comprising a compressible portion for protruding into adjacent pipe fittings so that when the volume in the pipe fittings expands, the compressible portion compresses to accommodate the expanded volume and resist rupture of the system.
 33. The fluid transport system of claim 24, wherein the integral pipe unit comprises a thermoplastic material.
 34. The fluid transport system of claim 33, wherein the thermoplastic material is polyvinyl chloride.
 35. The fluid transport system of claim 24, wherein the integral pipe unit comprises a metallic material.
 36. The fluid transport system of claim 24, wherein the integral pipe unit comprises an extruded material.
 37. The fluid transport system of claim 24, wherein the in tegral pipe unit comprises an injection molded material.
 38. The fluid transport system of claim 25, wherein the integral pipe unit and the plug at each end of the expansion channel comprise a smooth central passageway substantially free of surface irregularities adapted to transport liquid with a minimum of frictional losses.
 39. The fluid transport system of claim 25, wherein the system comprises a plurality of the plugs, further comprising a means for packaging the plurality of plugs and inserting one of the packaged plurality of plugs into each end of the expansion channel.
 40. The fluid transport system of claim 39, wherein the means for packaging and inserting plugs comprises a first length of the plurality of plugs having each of the plurality of plugs connected sequentially end to end by material adaptable for breaking, wherein a plug at the end of the first length of plugs is inserted into the end of the expansion channel and the inserted plug is broken away from the first length of plugs at the connecting material to provide a second length of plugs ready for repeating the insertion and breaking away steps.
 41. The fluid transport system of claim 24, wherein the fluid transport system is a plumbing system.
 42. The fluid transport system of claim 24, wherein the fluid transport system is a fire sprinkler system.
 43. The fluid transport system of claim 24, wherein the fluid transport system is an irrigation system.
 44. A fluid container having an internal volume, the container resistant to rupture due to expansion of the internal volume, comprising: a plurality of sides, one of the plurality of sides having a length and an inside surface and two adjacent edges along the length of the one side forming an open seam; a core structure connected to the inside surface and along the length of the one side and having an open seam contiguous with the open seam in the one side; and a hollow expansion channel along the length of the one side defined by the core structure, wherein the one side and the core structure comprise an integral unit, wherein the integral unit is expandable outwardly in the direction of the open seams, and wherein when the internal volume expands, the integral unit expands sufficiently to accommodate the expanded volume and resist rupture of the system.
 45. The fluid container of claim 44, the integral unit having an original non-expanded position, and the expanded internal volume is caused by freezing of fluid inside the container, wherein the integral unit comprises a configuration having elasticity sufficient to expand outwardly greater than the expanded internal volume caused by the freezing of the fluid and to contract to approximately the original non-expanded position when the frozen fluid thaws.
 46. The fluid container of claim 45, wherein the fluid inside the container is water and the integral unit is sufficiently expandable to accommodate an expanded volume of at least 10% when the water freezes.
 47. The fluid container of claim 44, the hollow expansion channel having open ends adaptable for sealing, the container further comprising a plug sealably contacting each end of the expansion channel.
 48. The fluid container of claim 47, wherein the plug is solid.
 49. The fluid container of claim 47, wherein the plug is hollow.
 50. The fluid container of claim 44, wherein the container comprises a thermoplastic material.
 51. The fluid container of claim 50, wherein the thermoplastic material is polyvinyl chloride.
 52. The fluid container of claim 44, wherein the container comprises a metallic material.
 53. The fluid container of claim 44, wherein the container comprises an extruded material.
 54. The fluid container of claim 44, wherein the container comprises an injection molded material.
 55. A fluid transport system having an internal volume, the system resistant to rupture due to expansion of the internal volume, comprising a pipe having a length and a pipe wall, the pipe having a center along the length of the pipe, the pipe wall comprising at least one depression toward the center and along the length of the pipe, each of the at least one depression defining an external expansion channel, wherein the pipe wall is expandable outwardly from the center of the pipe in the direction of the at least one depression, and wherein when the internal volume expands, the pipe wall expands sufficiently to accommodate the expanded volume and resist rupture of the system.
 56. The fluid transport system of claim 55, the pipe wall having an original non-expanded position, and the expanded internal volume is caused by freezing of fluid inside the system, wherein the pipe wall comprises a configuration having elasticity sufficient to expand outwardly greater than the expanded internal volume caused by the freezing of the fluid and to contract to approximately the original non-expanded position when the frozen fluid thaws.
 57. The fluid transport system of claim 56, wherein the fluid inside the system is water and the pipe wall is sufficiently expandable to accommodate an expanded volume of at least 10% when the water freezes.
 58. The fluid transport system of claim 55, the system further comprising an adapter for fitting the pipe to a conventional pipe, the adapter having a first end comprising a shape adapted to form a sealable fit with the pipe and a second end comprising a shape adapted to form a sealable fit with the conventional pipe.
 59. The fluid transport system of claim 58, the pipe having an end, wherein the first end of the adapter comprises an integral plug for sealably contacting the end of the expansion channel and wherein the first end of the adapter is larger than the pipe for sealably fitting over the end of the pipe.
 60. The fluid transport system of claim 58, the pipe being connectable to another pipe with pipe fittings, wherein the second end of the adapter comprises a shape adapted to form a sealable fit with the pipe fittings, the second end further comprising a compressible portion for protruding into adjacent pipe fittings so that when the volume in the pipe fittings expands, the compressible portion compresses to accommodate the expanded volume and resist rupture of the system. 